What Saved the Dinosaurs: Scientists Sniff Out Origin of Birds

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The ancestors of modern birds might have survived the mass
extinction that wiped out their dinosaur forebears by having a
better sense of smell, researchers suggest.

As birds evolved from small, feathered dinosaurs, scientists had
thought their sense of olfaction or smell got worse while their
vision, balance and coordination improved for flight.

"Scientists thought that parts of the brain were being dedicated
to these latter senses, while the region of the brain associated
with olfaction deteriorated through evolution," said researcher
Darla Zelenitsky, a paleontologist at the University of Calgary.

However, by analyzing skulls, one can deduce the size of the
brain region devoted to smell. It turns out early birds such as
Archaeopteryx
probably had as good a sense of smell as dinosaur relatives known
as theropods that were of similar size.

To see how the
sense of smell might have changed as birds evolved,
researchers analyzed 130 species of living birds, seven species
of fossil birds and 20 species of nonavian theropod dinosaurs,
which include carnivores such as velociraptors and giants such as
Tyrannosaurus rex. The team concentrated on the
dimensions of the animals' olfactory bulbs, the brain regions
underlying smell.

The researchers found the sense of smell improved overall during
the evolution of small theropods to modern
birds, apparently only decreasing much later on in some
lineages of birds less dependent on scent. The earliest birds
such as Archaeopteryx had a sense of smell comparable to
pigeons, while some "raptor" dinosaurs were as good as turkey
vultures, birds well known for their keen noses.

This improved sense of smell, as well as larger brains overall,
might have provided an edge that could explain why modern birds
are still around and their dinosaur and archaic bird relatives
are not.

"Since some modern-day birds are known to use their sense of
smell for foraging and for navigation, perhaps the combination of
flight and larger brains — including larger olfactory bulbs —
gave modern birds a competitive edge over archaic birds and other
dinosaurs to survive this
mass extinction," Zelenitsky told LiveScience.

The scientists detailed their findings online April 13 in the
journal Proceedings of the Royal Society B.